Learning word meanings in a first language should be a difficult task. The number and range of possible meanings to be learned is immense and, by some arguments, indeterminate from the typical information provided to young children. Despite these challenges, between 18- and 30-months-of-age the typical child's productive vocabulary increases tenfold. Many of the new words children learn at this age are nouns. Previous research suggests that the task of learning new nouns is made easier by biases or constraints that direct children's attention to the correct features of objects for name learning. Despite considerable empirical support for these word learning biases, however, little is known about their origins or the mechanisms by which they are implemented. This is the focus of the present proposal. The present study will test and augment a processed-based developmental account of how perceptual word learning biases develop. Specifically, the empirical studies proposed here are based on the proposal that the bias to attend shape young children demonstrate when learning names for novel solid objects is the developmental product of the early noun vocabulary. Thirteen studies will test specific predictions concerning the relation between young children's vocabularies, category knowledge, and the development of word learning biases. In so doing these studies will further our understanding of the mechanisms that support young children's smart word learning abilities. The present research has potential implications for developmental delays in language learning and specifically for children who evidence delays in learning words. Previous research in this area suggests that children given intensive exposure to sets of words designed to create a precocious word learning bias not only develop an early bias but show acceleration in their subsequent acquisition of new words outside the laboratory. This suggests the possibility of interventions to help children with delays in word learning. Before such interventions can be developed, however, much more needs to be known about the basic processes that support the development of word learning biases. Thus, the present research is designed to lay the foundation for the application of [unreadable] what is known about the development of word learning biases to children with delays in word learning. [unreadable] [unreadable]